It is the long term goal of the chemistry core to design and develop new classes of MRI contrast agents that are capable of reporting on in vivo anatomical properties of living organisms. The capacity to differentiate regions/tissues that may be magnetically similar but histologically distinct is a major impetus for the preparation of these agents. Current MRI agents are limited in their ability to target specific anatomical regions or cellular targets. The goal of this study is to develop and test new classes of contrast agents to facilitate microscopic MRI mapping of the brain. The agents will permit the long term analysis of cell movements and axonal projections in developing and adult brains. The approach will involve the synthesis of stable chelating agents that have been chemically modified so they can be attached to a variety of biomolecules. The design and synthesis of new contrast agents is divided into two parts: 1) the synthesis of a series of stable and chemically versatile complexes that are effective contrast agents and 2) selective attachment of these complexes to physiologically interesting moieties. These agents will be used in conjunction with Neuronal Connectivity Project and in the In Vivo Atlases Project. Together these approaches will provide the unprecedented ability to perform detailed axonal tracing of brain structure and axonal trajectories in both fixed and living brains.